This application claims the priority of German Patent Application Serial No. 100 50 561.9, filed Oct. 12, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to an integrated circuit (IC), and more particularly to an integrate circuit of a type having first circuit elements with a supply voltage which is equal to an external supply voltage of the IC, and with second circuit elements with a supply voltage which is smaller than the external supply voltage and is derived in form of an internal supply voltage from the first supply voltage.
Integrated circuits of this type are generally known. Those circuit elements are referred to above as first circuit elements are typically large structures that are arranged along the periphery of the IC and derive their power from an external power supply of typically 5 V. Those circuit elements referred to above as second circuit elements are primarily logic circuits with a high signal processing speed. To reduce electrical losses, the second circuit elements typically operate at a lower internal supply voltage of, for example, 3 V. The lower internal supply voltage is produced by a regulated voltage supply that is concealed from the outside. The regulator can include a voltage reference element, for example a Zener diode or a structure with an otherwise fixed band gap, a negatively coupled compensated feedback amplifier, and external support capacitors. Regulators of this type tend to be complex and experience a delay in activating the internal supply voltage after the external supply voltage is switched on. This delay is mainly caused by the external support capacitors.
It would therefore be desirable and advantageous to provide an improved integrated circuit which obviates prior art shortcomings and which is simple in structure and yet does not require additional external components and is able to supply internal power without noticeable delay after the external supply voltage is switched on.
According to one aspect of the present invention, an integrated circuit (IC) is proposed which includes first circuit elements, whose supply voltage is equal to the external supply voltage of the IC, and second circuit elements whose supply voltage is smaller than the external supply voltage and derived as an internal supply voltage from the first supply voltage. More particularly, the IC includes a first resistance voltage divider connected between the supply voltage terminal and the reference potential, an impedance transformer connected after the first resistance voltage divider, and a circuit for controlling the scalable voltage at the tap of the first resistance voltage divider as a function of the load.
It has been recognized that an integrated regulator for deriving the internal supply voltage can be omitted, because the external supply voltage is typically already stabilized to better than approximately +/xe2x88x9210%. It is therefore sufficient to derive the internal supply voltage from the external supply voltage and to keep the internal supply voltage constant within the stabilization limits of the external supply voltage and independent of the load.
According to one embodiment, the impedance transformer can be implemented as a drain-source channel of a first MOSFET connected between the supply voltage tap and an internal supply voltage terminal of the second circuit elements, with the gate of the MOSFET being connected to the tap of the first resistance voltage divider.
According to another embodiment, the circuit for load-dependent regulation of the partial voltage at the tap of the first resistance voltage divider can be a drain-source channel of a second MOSFET connected between the supply voltage tap and the internal supply voltage terminal, with the gate of the second MOSFET being connected to a tap of a second resistance voltage divider located between the supply voltage tap and the reference potential. A third MOSFET is connected in the drain line of the second MOSFET, which in conjunction with a fourth MOSFET connected between the supply voltage tap and the tap on the first resistance voltage divider forms a current mirror circuit.